The present invention relates to a process for the preparation of amidosilanes. These compounds have hitherto been prepared from organochlorosilanes and organic amides in the presence of a tertiary amine to capture liberated hydrochloric acid. Such a process is described in, for example, U.S. Pat. No. 2,876,234, U.S. Pat. No. 3,488,371 and German Published Specification No. 1,224,039. This process frequently leads to amidosilanes which, after removal of the solvent, are still so impure that they have to be purified by distillation or a thin-layer method. Large amounts of trialkylammonium salts are additionally produced, and their processing is likewise elaborate.
According to U.S. Pat. No. 3,776,933 and German Published Specification No. 2,319,818, amidosilanes can also be obtained from the alkali metal salts of the organic amides and organohalogenosilanes when alkali metals, such as sodium, finely divided in toluene are heated to reflux and excess amide is reacted therewith, accompanied with hydrogen being formed. This process has the disadvantage that the use of sodium metal is problematical concerning technical handling and that the formation of the metallated amide takes place slowly with the amide being exposed to detrimental thermal stress.
Thus, it is possible for N-benzoylbenzamidines to be formed irreversibly from ##STR3## on heating in toluene, and these unavoidably lead to product impurities.
Use of alkali metal has the additional disadvantage that, for safety reasons, even the smallest residues of unreacted metal must be completely removed before further processing of the reaction mixture.
The object of the present invention was to eliminate the disadvantages which have been mentioned.